I'd also like to ditto some of the other girls and give you an example of the reverse situtation. I'm 5'4" (and a half! ) and most other women my height are on 50cm and 52cm bikes. I ride a 44cm WSD compact frame. I have a long torso, but short arms and legs, so while I'm taller than my bike thinks I am...I needed the smaller frame to get the right top tube length.

It's hard to tell from the picture, but if your girlfriend has longer legs but a shorter torso, it's likely that she does need a WSD for the shorter top tube length.